The present invention is generally concerned with postage meters and mailing machines, and more particularly with improvements therein including apparatus for driving a postage meter drum.
In U.S. Pat. No. 4,287,825 issued Sept. 8, 1981 to Eckert, et al and assigned to the assignee of the present there is disclosed a postage value selection mechanism for selecting postage values which are to be printed by a rotary postage printing drum in a microcomputer controlled postage meter having a keyboard. The drive shaft of the drum includes a plurality of selectable racks, each of which is slidably movable in engagement with a print wheel within the drum for selectively rotating the print wheel for disposing one of its print elements at the outer periphery of the drum for printing purposes. The value selection mechanism includes a first stepper motor which is operable for selecting the respective racks, and a second stepper motor which is operable for actuating the selected rack for selectively rotating its associated print wheel. The microcomputer, which is coupled to the keyboard for processing postage value entries by an operator, selectively drives the respective stepper motors in response to keyboard entries.
In U.S. Pat. No. 2,934,009 issued Apr. 26, 1960 to Bach, et al and assigned to the assignee of the present invention there is described a postage meter which includes a drive mechanism comprising a single revolution clutch and a drive train for connecting the clutch to the postage meter drum. The clutch rotates the drum from a home position and into engagement with a letter fed to the drum. And the drum prints the pre-selected postage value on the letter while feeding the same downstream beneath the drum as the drum returns to the home position. Each revolution of the single revolution clutch and thus the drum, is initiated by the letter engaging a trip lever to release the helical spring of the single revolution clutch. The velocity versus time profile of the periphery of the drum approximates a trapezoidal configuration, having acceleration, constant velocity and deceleration portions, fixed by the particular clutch and drive train used in the application. This being the case, the throughput rate of any mailing machine associated with the meter is dictated by the cycling speed of the postage meter rather than by the speed with which the individual mailpieces are fed to the postage meter. Further, although the single revolution clutch structure has served as the workhorse of the industry for many years it has long been recognized that it is a complex mechanism which is relatively expensive to construct and maintain, does not precisely follow the ideal trapezoidal velocity vs. time motion profile which is preferred for drum motion, tends to be unreliable in high volume applications, and is noisy and thus irritating to customers. Accordingly:
An object of the invention is to replace the value selection mechanism of the prior art with a rotary value selection mechanism, having rotary rack selection means and rotary print element selection means, a stepper motor which selectively engages the respective rack and print element selection means, a D.C. motor, and a computer, wherein the computer is programmed for controlling the stepper motor to alternately select the rack or print element selection means, and for controlling the D.C. motor to drive the selected selection means in accordance with data representative of a desired trapezoidal-shaped velocity versus time profile;
Another object is to provide a D.C. motor, adapted to be coupled to any one of a plurality of loads, which is controlled by a computer which is programmed for driving the respective loads in accordance with various desired trapezoidal-shaped velocity versus time profiles of angular displacement of the motor shaft which are each representative of a desired linear displacement versus time profile of motion of a portion of a load;
Another object of the invention is to replace the postage meter drum drive mechanism of the prior art with the combination of a D.C. motor and a computer, and program the computer for causing the D.C. motor to drive the drum in accordance with an ideal trapezoidal-shaped velocity versus time profile which is a function of the input velocity of a mailpiece; and
Another object is to replace the trip lever as the drive initiating device and utilize in its place a pair of spaced apart sensing devices in the path of travel of a mailpiece fed to the postage meter, and program the computer to calculate the input velocity of a mailpiece, based upon the time taken for the mailpiece to traverse the distance between the sensing devices, and adjust both the time delay before commencing acceleration of the drum and the drum's acceleration, to cause the drum to timely engage the leading edge of the mailpiece.